How do you make a wallpaper texture?
Go to the Texture Paint workspace and do the following:

Create a new texture by pressing on + New button near the top.
Choose what ever settings you like.
Draw your texture of choice. Press N to see properties. Or right-click to get brush settings quickly.
After you are done go to the Shading workspace.
Select the object you want this texture on.
Choose a material for this object.
Create a image texture node. shift + a &gt;&gt; Texture &gt;&gt; Image Texture
Click on the Image Texture file drop-down. And choose the texture you made.
Connect the Color to Base Color.
Done!

Note: To view your changes in real-time as you are creating the texture you could do steps 4-9 right after you create your texture(before 3)